Motor vehicle and control method of motor vehicle

ABSTRACT

In a hybrid vehicle of the invention, in the event of specification that an exhaust treatment catalyst is in a preset adequate state at step S 112 , combustion control of an engine starts after a decrease of an intake pipe pressure P to a preset reference negative pressure Pref and reduction of an intake air flow into a cylinder of the engine by engine motoring. In the event of specification that the exhaust treatment catalyst is not in the preset adequate state but in an inadequate state at step S 112 , on the other hand, the combustion control of the engine immediately starts, prior to the decrease of the intake pipe pressure P to the preset reference negative pressure Pref. The hybrid vehicle of the invention allows an early start of the combustion control in a lower catalyst temperature condition that lowers the catalytic conversion power of the exhaust treatment catalyst and in a higher catalyst temperature condition that causes accelerated deterioration of the exhaust treatment catalyst in exposure to the air. The early start of the combustion control effectively reduces the potential shocks on a start of the engine, while preventing the potential troubles, for example, the worsened emission and the accelerated deterioration of the exhaust treatment catalyst, arising in the course of engine motoring due to the inadequate state of the exhaust treatment catalyst.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a motor vehicle and a control method of the motor vehicle.

2. Description of the Prior Art

One proposed technique for a motor vehicle equipped with an internal combustion engine performs combustion control of the internal combustion engine including fuel injection control and ignition control to restart the operation of the internal combustion engine, after an intake pipe pressure in an air intake conduit of the internal combustion engine decreases to a sufficient negative pressure by motoring the internal combustion engine (see, for example, Japanese Patent Laid-Open Gazette No. 2001-304007). This prior art motor vehicle delays the combustion control until a sufficient decrease in amount of the air in the air intake conduit and a cylinder of the internal combustion engine. The delayed combustion control reduces the potential shocks on a start of the internal combustion engine, compared with the combustion control including fuel injection control and ignition control immediately after the engine motoring.

This prior art motor vehicle certainly reduces the potential shocks on a start of the internal combustion engine but does not take into account the state of an exhaust treatment catalyst, which treats the exhaust of the internal combustion engine to convert harmful components of the exhaust into harmless components. The prior art motor vehicle delays the start timing of the combustion control until the engine motoring decreases the intake pipe pressure in the air intake conduit of the internal combustion engine to the sufficient negative pressure. In a low temperature condition, the exhaust treatment catalyst is generally not active and does not exert the sufficient catalytic conversion power. In the case where the air in the air intake conduit and in the cylinder has an uncombusted fuel content, for example, in the event of slow leakage of the fuel from an injector for injecting the fuel under the operation stop condition of the internal combustion engine, the exhaust treatment catalyst in the low temperature condition may not succeed in sufficiently converting the uncombusted fuel content for a relatively long time. During motoring of the internal combustion engine, the air in the air intake conduit and the cylinder is directly flowed to the exhaust treatment catalyst. In a high temperature condition of the exhaust treatment catalyst, the delayed start timing of the combustion control extends the time of exposure of the exhaust treatment catalyst to the air and may accelerate deterioration of the exhaust treatment catalyst. As described above, the delayed start timing of the combustion control under some conditions of the exhaust treatment catalyst may cause the worsened emission or the accelerated deterioration of the exhaust treatment catalyst.

SUMMARY OF THE INVENTION

The object of the invention is thus to eliminate the drawbacks of the prior art technique and to provide a motor vehicle that reduces potential shocks on a start of an internal combustion engine and prevents potential troubles arising under some conditions of an exhaust treatment catalyst, as well as to a corresponding control method of such a motor vehicle.

In order to attain at least part of the above and the other related objects, the present invention is constructed as follows.

The present invention is directed to a motor vehicle including: a motoring device that is capable of motoring an internal combustion engine; an exhaust treatment catalyst that treats exhaust of the internal combustion engine to convert harmful components of the exhaust into harmless components; a catalyst state detection unit that detects a state of the exhaust treatment catalyst; an in-cylinder air flow specification module that specifies whether an intake air flow into a cylinder of the internal combustion engine decreases to a preset low range; and an internal combustion engine start control module that starts combustion control of the internal combustion engine, in response to requirement for a restart of the internal combustion engine. When the state of the exhaust treatment catalyst detected by the catalyst state detection unit is a preset adequate state, the internal combustion engine start control module starts the combustion control of the internal combustion engine after specification of a decrease in intake air flow into the cylinder of the internal combustion engine to the preset low range by the in-cylinder air flow specification module in the course of motoring the internal combustion engine by the motoring device. When the state of the exhaust treatment catalyst detected by the catalyst state detection unit is not the preset adequate state but is an inadequate state, the internal combustion engine start control module immediately starts the combustion control of the internal combustion engine, prior to specification of a decrease in intake air flow into the cylinder of the internal combustion engine to the preset low range by the in-cylinder air flow specification module in the course of motoring the internal combustion engine by the motoring device.

In the preset adequate state of the exhaust treatment catalyst, the motor vehicle of the invention starts the combustion control of the internal combustion engine to restart the operation of the internal combustion engine, after the intake air flow into the cylinder decreases to the preset low range in the course of motoring the internal combustion engine. This desirably reduces the potential shocks on a start of the internal combustion engine. In the inadequate state of the exhaust treatment catalyst, on the other hand, the motor vehicle of the invention immediately starts the combustion control of the internal combustion engine, prior to a decrease of the intake air flow into the cylinder to the preset low range. This may not sufficiently reduce the potential shocks on a start of the internal combustion engine but effectively prevents the potential troubles caused by a delayed start timing of the combustion control in the course of engine motoring in the inadequate state of the exhaust treatment catalyst. The low range may be set experimentally or otherwise to a specific level of the intake air flow into the cylinder, which restrains the driver from feeling uncomfortable by the shocks in the combustion control after engine motoring on a start of the internal combustion engine.

In the motor vehicle of the invention, the preset low range may represent a certain level of the intake air flow into the cylinder that is equivalent to idling operation of the internal combustion engine. This arrangement ensures a smooth start of the internal combustion engine without causing an engine stall and effectively reduces the potential shocks on a start of the internal combustion engine.

In one preferable embodiment of the motor vehicle of the invention, the in-cylinder air flow specification module includes an intake pipe pressure specification module, which determines whether an intake pipe pressure of the internal combustion engine decreases to a preset reference negative pressure and thereby specifies whether the intake air flow into the cylinder of the internal combustion engine decreases to the preset low range. The lower intake air flow into the cylinder tends to decrease the intake pipe pressure. Namely the intake air flow into the cylinder is correlated to the intake pipe pressure. The intake air flow into the cylinder is thus estimable from the measured intake pipe pressure.

The present invention is also directed to another motor vehicle including: a motoring device that is capable of motoring an internal combustion engine; an exhaust treatment catalyst that treats exhaust of the internal combustion engine to convert harmful components of the exhaust into harmless components; a catalyst state detection unit that detects a state of the exhaust treatment catalyst; an intake pipe pressure specification module that specifies whether an intake pipe pressure of the internal combustion engine decreases to a preset reference negative pressure; and an internal combustion engine start control module that starts combustion control of the internal combustion engine, in response to requirement for a restart of the internal combustion engine. When the state of the exhaust treatment catalyst detected by the catalyst state detection unit is a preset adequate state, the internal combustion engine start control module starts the combustion control of the internal combustion engine after specification of a decrease in intake pipe pressure of the internal combustion engine to the preset reference negative pressure by the intake pipe pressure specification module in the course of motoring the internal combustion engine by the motoring device. When the state of the exhaust treatment catalyst detected by the catalyst state detection unit is not the preset adequate state but is an inadequate state, the internal combustion engine start control module immediately starts the combustion control of the internal combustion engine, prior to specification of a decrease in intake pipe pressure of the internal combustion engine to the preset reference negative pressure by the intake pipe pressure specification module in the course of motoring the internal combustion engine by the motoring device.

In the preset adequate state of the exhaust treatment catalyst, the motor vehicle of the invention starts the combustion control of the internal combustion engine to restart the operation of the internal combustion engine, after the intake pipe pressure decreases to the preset reference negative pressure in the course of motoring the internal combustion engine. This desirably reduces the potential shocks on a start of the internal combustion engine. In the inadequate state of the exhaust treatment catalyst, on the other hand, the motor vehicle of the invention immediately starts the combustion control of the internal combustion engine, prior to a decrease of the intake pipe pressure to the preset reference negative pressure. This may not sufficiently reduce the potential shocks on a start of the internal combustion engine but effectively prevents the potential troubles caused by a delayed start timing of the combustion control in the course of engine motoring in the inadequate state of the exhaust treatment catalyst. The reference negative pressure may be set experimentally or otherwise to a specific pressure level, which restrains the driver from feeling uncomfortable by the shocks in the combustion control after engine motoring on a start of the internal combustion engine.

In the motor vehicle of the invention, the preset reference negative pressure may represent a certain level of the intake pipe pressure that is equivalent to idling operation of the internal combustion engine. This arrangement ensures a smooth start of the internal combustion engine without causing an engine stall and effectively reduces the potential shocks on a start of the internal combustion engine.

In one preferable structure of the motor vehicle of the invention, the intake pipe pressure specification module specifies whether the intake pipe pressure of the internal combustion engine decreases to the preset reference negative pressure, based on a specific parameter in correlation to the intake pipe pressure of the internal combustion engine. This structure does not require direct measurement of the intake pipe pressure. The specific parameter may be a motoring time of the internal combustion engine by the motoring device. The longer motoring time tends to decrease the intake pipe pressure to a greater negative pressure. The motoring time is thus the parameter correlated to the intake pipe pressure.

In one preferable application of the motor vehicle of the invention, the catalyst state detection unit detects the inadequate state of the exhaust treatment catalyst, when the exhaust treatment catalyst has a temperature in a low temperature range that allows exertion of only an insufficient catalytic conversion power. Such definition enables an early start of the combustion control in the low catalyst temperature range where the exhaust treatment catalyst has the insufficient catalytic conversion power. This application of the invention effectively prevents extension of an undesirable emission time period when the uncombusted fuel content remaining in an air intake conduit or the cylinder of the internal combustion engine is not sufficiently converted by the exhaust treatment catalyst bus is directly discharged to the outside air. This arrangement thus desirably prevents the worsened emission. The low temperature range represents a certain temperature condition of the exhaust treatment catalyst that is below a required activation temperature or just reaches the required activation temperature but still has only an insufficient level of the catalytic conversion power. The low temperature range may be determined experimentally or empirically.

In another preferable application of the motor vehicle of the invention, the catalyst state detection unit detects the inadequate state of the exhaust treatment catalyst, when the exhaust treatment catalyst has a temperature in a high temperature range that causes quick deterioration of the exhaust treatment catalyst by exposure to the air. Such definition enables an early start of the combustion control in the high catalyst temperature range. This application of the invention effectively restrains the exhaust treatment catalyst from being excessively exposed to the air flowed to the exhaust treatment catalyst by engine motoring and thus prevents the accelerated deterioration of the exhaust treatment catalyst. The high temperature range represents a certain temperature condition of the exhaust treatment catalyst that accelerates deterioration of the exhaust treatment catalyst in exposure to the air. The high temperature range may be determined experimentally or empirically.

In one preferable embodiment of the invention, the motor vehicle further includes an internal combustion engine stop control module that stops the operation of the internal combustion engine upon satisfaction of a preset internal combustion engine auto stop condition. The internal combustion engine start control module restarts the internal combustion engine upon satisfaction of a preset internal combustion engine auto start condition after the stop of the operation of the internal combustion engine by the internal combustion engine stop control module. In motor vehicles with auto stop and auto restart functions of the internal combustion engine, the internal combustion engine repeats stopping and restarting frequently during a drive. This arrangement is preferably applicable to the motor vehicles with such functions.

In the motor vehicle of this preferable embodiment, the internal combustion engine stop control module may prohibit the stop of the internal combustion engine when the exhaust treatment catalyst is not in the preset adequate state during operation of the internal combustion engine. This arrangement desirably reduces the frequency of restarting the operation of the internal combustion engine in the inadequate state of the exhaust treatment catalyst.

The present invention is further directed to a control method of a motor vehicle, including the steps of: (a) detecting a state of an exhaust treatment catalyst that treats exhaust of the internal combustion engine to convert harmful components of the exhaust into harmless components; and (b) when the state of the exhaust treatment catalyst detected by the step (a) is a preset adequate state, starting the combustion control of the internal combustion engine after specification of a decrease in intake air flow into the cylinder of the internal combustion engine to the preset low range in the course of motoring the internal combustion engine, and when the state of the exhaust treatment catalyst detected by the step (a) is not the preset adequate state but is an inadequate state, starting the combustion control of the internal combustion engine, prior to specification of a decrease in intake air flow into the cylinder of the internal combustion engine to the preset low range in the course of motoring the internal combustion engine.

In the preset adequate state of the exhaust treatment catalyst, the control method of the invention starts the combustion control of the internal combustion engine to restart the operation of the internal combustion engine, after the intake air flow into the cylinder decreases to the preset low range in the course of motoring. This desirably reduces the potential shocks on a start of the internal combustion engine. In the inadequate state of the exhaust treatment catalyst, on the other hand, the control method of the invention starts the combustion control of the internal combustion engine, prior to a decrease of the intake air flow into the cylinder to the preset low range. This may not sufficiently reduce the potential shocks on a start of the internal combustion engine but effectively prevents the potential troubles caused by a delayed start timing of the combustion control in the course of engine motoring in the inadequate state of the exhaust treatment catalyst. This control method may further include steps for actualizing the additional functions described above in connection with the motor vehicle of the invention.

The present invention is further directed to another control method of a motor vehicle, comprising the steps of: (a) detecting a state of an exhaust treatment catalyst that treats exhaust of the internal combustion engine to convert harmful components of the exhaust into harmless components; and (b) when the state of the exhaust treatment catalyst detected by the step (a) is a preset adequate state, starting the combustion control of the internal combustion engine after specification of a decrease in intake pipe pressure of the internal combustion engine to the preset reference negative pressure in the course of motoring the internal combustion engine, and when the state of the exhaust treatment catalyst detected by the step (a) is not the preset adequate state but is an inadequate state, starting the combustion control of the internal combustion engine, prior to specification of a decrease in intake pipe pressure of the internal combustion engine to the preset reference negative pressure in the course of motoring the internal combustion engine.

In the preset adequate state of the exhaust treatment catalyst, the control method of the invention starts the combustion control of the internal combustion engine to restart the operation of the internal combustion engine, after the intake pipe pressure decreases to the preset reference negative pressure in the course of motoring the internal combustion engine. This desirably reduces the potential shocks on a start of the internal combustion engine. In the inadequate state of the exhaust treatment catalyst, on the other hand, the control method of the invention starts the combustion control of the internal combustion engine, prior to a decrease of the intake pipe pressure to the preset reference negative pressure. This may not sufficiently reduce the potential shocks on a start of the internal combustion engine but effectively prevents the potential troubles caused by a delayed start timing of the combustion control in the course of engine motoring in the inadequate state of the exhaust treatment catalyst. This control method may further include steps for actualizing the additional functions described above in connection with the motor vehicle of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates the configuration of a hybrid vehicle;

FIG. 2 schematically illustrates the configuration of an engine;

FIG. 3 is a flowchart showing a start control routine;

FIG. 4 is an example of a torque demand setting map;

FIG. 5 is a graph showing variations of torque command Tm1* against time elapsed since a start of motoring;

FIG. 6 is an alignment chart that explains dynamics of rotational elements in a power distribution integration mechanism 30.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

One mode of carrying out the invention is described below as a preferred embodiment with reference to the accompanied drawings. FIG. 1 schematically illustrates the configuration of a hybrid vehicle 20 in one embodiment of the invention. As shown in FIG. 1, the hybrid vehicle 20 of the embodiment includes an engine 22, an engine electronic control unit 50 (engine ECU 50) that controls the operations of the whole engine system, a three shaft-type power distribution integration mechanism 30 that is linked to a crankshaft 26 or an output shaft of the engine 22 via a damper 28, a motor MG1 that is connected to the power distribution integration mechanism 30 and has power generation capability, a reduction gear 35 that is attached to a ring gear shaft 32 a or a driveshaft linked with the power distribution integration mechanism 30, a motor MG2 that is connected to the reduction gear 35, and a hybrid electronic control unit 70 that controls the operations of the whole hybrid vehicle 20. As illustrated in FIG. 2, the hybrid vehicle 20 also has a catalytic converter 160 located downstream the engine 22 to treat the exhaust and convert harmful components of the exhaust into harmless components.

The engine 22 is an internal combustion engine that consumes a hydrocarbon fuel, such as gasoline or light oil, to output power. As shown in FIG. 2, the air cleaned by an air cleaner 122 and taken in via a throttle valve 124 is mixed with the atomized gasoline injected by an injector 126 to the air-fuel mixture. The air-fuel mixture is introduced into a cylinder 150 via an intake valve 128. The introduced air-fuel mixture is ignited with spark made by a spark plug 130 to be explosively combusted. The reciprocating motions of a piston 132 by the combustion energy are converted into rotational motions of the crankshaft 26. The throttle valve 124 varies an inclination angle (opening) relative to the cross section of an air intake conduit 121 to regulate the air flow through the air intake conduit 121. An actuator 136 is actuated to electrically vary the opening of the throttle valve 124. The opening of the throttle valve 124 is measured by a throttle position sensor 146 and is output to the engine ECU 50. The exhaust from the engine 22 goes through the catalytic converter 160 that converts toxic components included in the exhaust, that is, carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx), into harmless components, and is discharged to the outside air.

The catalytic converter 160 is connected with an exhaust conduit 123 and is filled with an exhaust treatment catalyst 161. A typical example of the exhaust treatment catalyst 161 is a three-way catalyst that mainly consists of an oxidation catalyst, such as platinum (Pt) or palladium (Pd), a reduction catalyst, such as rhodium (Rh), and an assisting catalyst, such as ceria (CeO₂). The functions of the oxidation catalyst convert CO and HC into water (H₂O) and carbon dioxide (CO₂). The functions of the reduction catalyst convert NOx into nitrogen (N₂) and oxygen (O₂). A temperature sensor 162 is attached to the catalytic converter 160 to monitor the temperature of the exhaust treatment catalyst 161.

The engine ECU 50 is constructed as a microprocessor including a CPU, a ROM that stores processing programs, a RAM that temporarily stores data, and input and output ports, which are not specifically illustrated. The engine ECU 50 receives, via its input port, signals from various sensors that measure and detect the conditions of the engine 22. The signals input into the engine ECU 50 include a throttle opening from the throttle position sensor 146, an air intake flow into the engine 22 from a vacuum sensor 148, pulse signals from a crank angle sensor 140, and a catalyst temperature from the temperature sensor 162. The engine ECU 50 outputs, via its output port, diverse control signals and driving signals to drive and control the engine 22. The signals output from the engine ECU 50 include driving signals to the actuator 136 for actuating the throttle valve 124, driving signals to the injector 126, and control signals to an ignition coil 138 integrated with an igniter to control the spark by the spark plug 130. The engine ECU 50 is electrically connected with the hybrid electronic control unit 70 to drive and control the engine 22 in response to control signals received from the hybrid electronic control unit 70 and to output data regarding the operating conditions of the engine 22 to the hybrid electronic control unit 70 according to the requirements.

The power distribution integration mechanism 30 has a sun gear or external gear 31, a ring gear or internal gear 32 that is arranged concentrically with the sun gear 31, multiple pinion gears 33 that engage with both the sun gear 31 and the ring gear 32, and a carrier 34 that holds the multiple pinion gears 33 to allow their revolutions and rotations on their axes. The power distribution integration mechanism 30 is constructed as a planetary gear mechanism that has differential motions with the sun gear 31, the ring gear 32, and the carrier 34 as rotating elements. When the motor MG1 functions as an electric generator, the power output from the engine 22 and transmitted through the carrier 34 is distributed to the sun gear 31 and the ring gear 32 at their gear ratio. When the motor MG1 functions as an electric motor, on the other hand, the power output from the engine 22 and transmitted through the carrier 34 is integrated with the power output from the motor MG1 and transmitted through the sun gear 31 and is output to the ring gear 32. The power output to the ring gear 32 is accordingly transmitted to drive wheels 63 via a ring gear shaft 32 a, the gear mechanism 60, and the differential gear 62.

Both the motors MG1 and MG2 are known synchronous motor generators that are driven as a generator and as a motor. The motors MG1 and MG2 transmit electric power to and from a battery 55 via inverters 41 and 42. Power lines 54 that connect the inverters 41 and 42 with the battery 55 are constructed as a positive electrode bus line and a negative electrode bus line shared by the inverters 41 and 42. This arrangement enables the electric power generated by one of the motors MG1 and MG2 to be consumed by the other motor. The motor MG1 also functions as a starter to rotate the crank shaft 26 of the engine 22 at the time of starting the engine. Operations of both the motors MG1 and MG2 are controlled by a motor electronic control unit (hereinafter, referred to as motor ECU) 40. The motor ECU 40 receives diverse signals required for controlling the operations of the motors MG1 and MG2, for example, signals from rotational position detection sensors 43 and 44 that detect the rotational positions of rotors in the motors MG1 and MG2 and phase currents applied to the motors MG1 and MG2 and measured by non-illustrated current sensors. The motor ECU 40 outputs switching control signals to the inverters 41 and 42. The motor ECU 40 communicates with the hybrid electronic control unit 70 to control operations of the motors MG1 and MG2 in response to control signals transmitted from the hybrid electronic control unit 70 while outputting data relating to the operating conditions of the motors MG1 and MG2 to the hybrid electronic control unit 70 according to the requirements.

The battery 55 is under control of a battery electronic control unit (hereinafter, referred to as a battery ECU) 56. The battery ECU 56 receives diverse signals required for control of the battery 55, for example, an inter-terminal voltage measured by a non-illustrated voltage sensor disposed between terminals of the battery 55, a charge-discharge current measured by a non-illustrated current sensor attached to the power line 54 connected with the output terminal of the battery 55, and a battery temperature measured by a temperature sensor 57 attached to the battery 55. The battery ECU 56 outputs data relating to the state of the battery 55 to the hybrid electronic control unit 70 according to the requirements. The battery ECU 56 calculates a state of charge (SOC) of the battery 55, based on the accumulated charge-discharge current measured by the current sensor, for control of the battery 55.

The hybrid electronic control unit 70 is constructed as a microprocessor including a CPU 72, a ROM 74 that stores processing programs, a RAM 76 that temporarily stores data, a non-illustrated input-output port, and a non-illustrated communication port. The hybrid ECU 70 receives various signals via the input port: an ignition signal from an ignition switch 80, a gearshift position SP from a gearshift position sensor 82 that detects the current position of a gearshift lever 81, an accelerator opening Acc from an accelerator pedal position sensor 84 that measures a step-on amount of an accelerator pedal 83, a brake pedal position BP from a brake pedal position sensor 86 that measures a step-on amount of a brake pedal 85, and a vehicle speed V from a vehicle speed sensor 88. The hybrid electronic control unit 70 is connected with the engine ECU 50, the motor ECU 40, and the battery ECU 56 via the communication port and transmits diverse control signals and data to and from the engine ECU 50, the motor ECU 40, and the battery ECU 56, as mentioned above.

The hybrid vehicle 20 of the embodiment thus constructed calculates a torque demand to be output to the ring gear shaft 32 a functioning as the drive shaft, based on observed values of a vehicle speed V and an accelerator opening Acc, which corresponds to a driver's step-on amount of the accelerator pedal 83. The engine 22 and the motors MGl and MG2 are subjected to operation control to output a required level of power corresponding to the calculated torque demand to the ring gear shaft 32 a. The operation control of the engine 22 and the motors MG1 and MG2 selectively effectuates one of a torque conversion drive mode, a charge-discharge drive mode, and a motor drive mode. The torque conversion drive mode controls the operations of the engine 22 to output a quantity of power equivalent to the required level of power, while driving and controlling the motors MG1 and MG2 to cause all the power output from the engine 22 to be subjected to torque conversion by means of the power distribution integration mechanism 30 and the motors MG1 and MG2 and output to the ring gear shaft 32 a. The charge-discharge drive mode controls the operations of the engine 22 to output a quantity of power equivalent to the sum of the required level of power and a quantity of electric power consumed by charging the battery 55 or supplied by discharging the battery 55, while driving and controlling the motors MG1 and MG2 to cause all or part of the power output from the engine 22 equivalent to the required level of power to be subjected to torque conversion by means of the power distribution integration mechanism 30 and the motors MG1 and MG2 and output to the ring gear shaft 32 a, simultaneously with charge or discharge of the battery 55. The motor drive mode stops the operations of the engine 22 and drives and controls the motor MG2 to output a quantity of power equivalent to the required level of power to the ring gear shaft 32 a.

The description regards the operations of the hybrid vehicle 20 having the configuration discussed above, especially a series of control to restart the operation of the engine 22, for example, in response to a shift of the drive mode from the motor drive mode to the torque conversion drive mode or to the charge-discharge drive mode. FIG. 3 is a flowchart showing a start control routine executed by the hybrid electronic control unit 70. This start control routine is performed on a start of the engine 22.

In the start control routine of FIG. 3, the CPU 72 of the hybrid electronic control unit 70 first inputs required data for start control, that is, the accelerator opening Acc from the accelerator pedal position sensor 84, the vehicle speed V from the vehicle speed sensor 87, a rotation speed Ne of the engine 22, rotation speeds Nm1 and Nm2 of the motors MG1 and MG2, a time t elapsed since a start of motoring the engine 22, and an output limit Wout of the battery 55 (step S100). The rotation speed Ne of the engine 22 is computed in response to signals output from the crank angle sensor 140 attached to the crankshaft 26 and is received from the engine ECU 50 by communication. The rotation speeds Nm1 and Nm2 of the motors MG1 and MG2 are computed from the rotational positions of the respective rotors in the motors MG1 and MG2 detected by the rotational position detection sensors 43 and 44 and are received from the motor ECU 40 by communication. The time t elapsed since a start of motoring the engine 22 is input as the count of a timer, which starts counting time in response to a start request of the engine 22. The output limit Wout of the battery 55 is set corresponding to the temperature Tb of the battery 55 measured by the temperature sensor 57 and the state of charge SOC of the battery 55 and is received from the battery ECU 56 by communication.

After the data input, the CPU 72 sets a torque demand Tr* to be output to the ring gear shaft 32 a or the driveshaft, based on the input accelerator opening Acc and the input vehicle speed V (step S102). A concrete procedure of setting the torque demand Tr* in this embodiment stores in advance variations in torque demand Tr* against the accelerator opening Acc and the vehicle speed V as a torque demand setting map in the ROM 74 and reads the torque demand Tr* corresponding to the given accelerator opening Acc and the given vehicle speed V from this torque demand setting map. One example of the torque demand setting map is shown in FIG. 4.

The CPU 72 subsequently sets a torque command Tm1* of the motor MG1, based on the input time t elapsed since a start of motoring the engine 22 (step S104). A concrete procedure of setting the torque command Tm1* of the motor MG1 in this embodiment stores in advance a variation in torque command Tm1* against the time t elapsed since a start of motoring as a torque command setting map in the ROM 74 and reads the torque command Tm1* corresponding to the given time t elapsed since a start of motoring from this torque command setting map. One example of the torque command setting map is shown in FIG. 5. As shown in the map of FIG. 5, the torque command Tm1* of the motor MG1 gradually increases from a time t0 when a start request of the engine 22 is output, and reaches a preset relatively high torque level T1 at a time t1. The torque command Tm1* is kept at the preset relatively high torque level T1 for a preset time period between the time t1 and a time t2 and gradually decreases to reach a preset torque level T2 at a time t3. The torque level T1 and the time period between the time t1 and the time t2 are set as a torque and a time length that ensure a quick increase in rotation speed Ne of the engine 22, and depend upon the performances of the engine 22 and the battery 55. The torque level T2 is set as a torque that further increases the rotation speed Ne of the engine 22 while saving the power consumption for motoring, and depends upon the performances of the engine 22 and the battery 55. The torque command Tm1* of the motor MG1 is set to make the rotation speed Ne of the engine 22 increase to and subsequently kept at a preset starting rotation speed Nstart.

The CPU 72 then determines whether the rotation speed Ne of the engine 22 reaches or exceeds the preset starting rotation speed Nstart (step S106). Immediately after output of the start request of the engine 22, the rotation speed Ne of the engine 22 is lower than the preset starting rotation speed Nstart. In this state, a negative answer is given at step S106 and the processing flow goes to step S116. At step S116, the CPU 72 calculates an upper torque restriction Tmax as a maximum possible torque output from the motor MG2 according to Equation (1) given below. The calculation subtracts the product of the torque command Tm1* and the rotation speed Nm1 of the motor MG1, which represents the power consumption of the motor MG1, from the output limit Wout of the battery 55 and divides the difference by the rotation speed Nm2 of the motor MG2: Tmax=(Wout−Tm1*−Nm1)/Nm2   (1)

The CPU 72 then calculates a tentative motor torque Tm2tmp as a torque to be output from the motor MG2 from the torque demand Tr*, the torque command Tm1* of the motor MG1, a gear ratio p of the power distribution integration mechanism 30, and a gear ratio Gr of the reduction gear 35 according to Equation (2) given below (step S118): Tm2tmp=(Tr*+Tm1*/p)/Gr   (2) The CPU 72 compares the calculated upper torque restriction Tmax with the calculated tentative motor torque Tm2tmp and sets the smaller to a torque command Tm2* of the motor MG2 (step S120). Such setting of the torque command Tm2* of the motor MG2 enables the output torque of the motor MG2 to cancel out a reactive torque applied to the ring gear shaft 32 a or the driveshaft while the motor MG1 is motoring the engine 22. The torque demand Tr* to be output to the ring gear shaft 32 a is restricted to the output limit of the battery 55.

Equation (2) given above is readily led from an alignment chart of FIG. 6. In the alignment chart of FIG. 6, the left axis ‘S’ represents the rotation speed of the sun gear 31 that is equivalent to the rotation speed Nm1 of the motor MG1. The middle axis ‘C’ represents the rotation speed of the carrier 34 that is equivalent to the rotation speed Ne of the engine 22. The right axis ‘R’ represents the rotation speed Nr of the ring gear 32 that is equivalent to division of the rotation speed Nm2 of the motor MG2 by the gear ratio Gr of the reduction gear 35. The thick arrows on the axis ‘S’ and the axis ‘R’ represent torques applied to the respective axes. In the state of the current processing flow, the engine 22 has not yet started its operation and applies no torque to the carrier 34. The crankshaft 26 of the engine 22 is supported by the torque of the motor MG1 (torque command Tm1*) applied to the sun gear 31. The ring gear shaft 32 a receives application of a reactive torque, and the motor MG2 outputs a cancellation torque (=−Tm1*/p) to cancel out the reactive torque.

After setting the torque commands Tm1* and Tm2* of the motors MG1 and MG2 in the above manner, the CPU 72 sends the torque commands Tm1* and Tm2* to the motor ECU 40 (step S122). The motor ECU 40 receives the torque commands Tm1* and Tm2* and performs switching control of the switching elements included in the respective inverters 41 and 42 to drive the motor MG1 with the torque command Tm1* and the motor MG2 with the torque command Tm2*. The CPU 72 then specifies whether the start of the engine 22 is complete or incomplete (step S124) The specification of the complete or incomplete start of the engine 22 is based on determination of whether the rotation speed Ne of the engine 22 exceeds a reference speed Nref, which is higher than the starting rotation speed Nstart by a predetermined level. In the state of the current processing flow, the rotation speed Ne of the engine 22 is still lower than the starting rotation speed Nstart, and the engine ECU 50 has not yet started combustion control of the engine 22 including fuel injection control and ignition control. Namely the CPU 72 specifies incomplete start of the engine 22 at step S124 and returns the processing flow to step S100.

The rotation speed Ne of the engine 22 reaches or exceeds the preset starting rotation speed Nstart during the repeated execution of steps S100 to S106 and S116 to S124. In this state, an affirmative answer is given at step S106 and the processing flow goes to step S108. The CPU 72 determines whether an intake pipe pressure P is lower than a preset reference negative pressure Pref (step S108). This specifies whether the intake air flow into the cylinder 150 decreases to a preset low range. The reference negative pressure Pref is set to a negative pressure level that is equivalent to the idling operation of the engine 22. In this embodiment, the result of the comparison between the intake pipe pressure P and the preset reference negative pressure Pref at step S108 is based on the determination of whether the time t elapsed since a start of motoring exceeds a predetermined reference time length, for example, 2 to 3 seconds. The reference time length is experimentally or empirically determined as a required time period from a start of motoring for decreasing the intake pipe pressure P to the preset reference negative pressure Pref. Immediately after the rotation speed Ne of the engine 22 reaches the preset starting rotation speed Nstart, the time t elapsed since a start of motoring has not yet exceeded the preset reference time length. Namely the intake pipe pressure P has not yet decreased to the preset reference negative pressure Pref. In this state, a negative answer is given at step S108 and the processing flow goes to step S112. The CPU 72 specifies whether the exhaust treatment catalyst 161 is in an adequate state (step S112). In this embodiment, the exhaust treatment catalyst 161 having the temperature in a specific temperature range between a preset low reference temperature and a preset high reference temperature is specified as the exhaust treatment catalyst 161 in the adequate state. The low reference temperature represents a lower threshold temperature, below which the catalytic conversion power of the exhaust treatment catalyst 161 is insufficient. The high reference temperature represents a higher threshold temperature, above which the exposure of the exhaust treatment catalyst 161 to the air causes the excessively particle growth of the exhaust treatment catalyst 161, which undesirably reduces the surface area of the exhaust treatment catalyst 161 and accelerates deterioration of the exhaust treatment catalyst 161. When the temperature of the exhaust treatment catalyst 161 is within the specific temperature range between the preset low reference temperature and the preset high reference temperature, an affirmative answer is given to step S112. The processing flow then executes steps S116 to S122 and specifies whether the start of the engine 22 is complete or incomplete at step S124. In this state, the start of the engine 22 is still incomplete since the engine ECU 50 has not yet started the combustion control of the engine 22. A negative answer is accordingly given at step S124 and the processing flow goes back to step S100. In the adequate state of the exhaust treatment catalyst 161, motoring of the engine 22 continues until the intake pipe pressure P of the air intake conduit 121 reaches the preset reference negative pressure Pref. During this engine motoring, the internal air of the air intake conduit 121 and the cylinder 150 is flowed to the exhaust treatment catalyst 161. The exhaust treatment catalyst 161 converts the uncombusted fuel content in the air flow, prior to discharge to the outside air. This prevents the worsened emission and the accelerated deterioration of the exhaust treatment catalyst 161 due to the air-induced particle growth.

The intake pipe pressure P decreases to be lower than the preset reference negative pressure Pref during the repeated execution of steps S100 to S108, S112, and S116 to S124. In this state, an affirmative answer is given at step S108 and the processing flow goes to step S110. The CPU 72 specifies execution or no-execution of combustion control of the engine 22 including fuel injection control and ignition control (step S110). Immediately after the intake pipe pressure P decreases below the preset reference negative pressure Pref, the engine ECU 50 has not yet started the combustion control of the engine 22. In this state, a negative answer is given at step S110 and the processing flow goes to step S114. The CPU 72 instructs the engine ECU 50 to start the combustion control (step S114). The engine ECU 50 starts the combustion control of the engine 22 in response to this instruction. In this state, the intake pipe pressure P is lower than the preset reference negative pressure Pref, and the intake air flow into the cylinder 150 decreases to the preset low range. The combustion control of the engine 22 in this state reduces the potential shocks on a start of the engine 22, compared with the combustion control of the engine 22 immediately after the increase of the rotation speed Ne of the engine 22 to the preset starting rotation speed Nstart, that is, under the condition of the intake pipe pressure P of not lower than the preset reference negative pressure Pref. The processing flow then executes steps S116 to S122 and specifies whether the start of the engine 22 is complete or incomplete at step S124. In this state, the start of the engine 22 is still incomplete since the engine ECU 50 has just started the combustion control of the engine 22. A negative answer is thus given again at step S124 and the processing flow goes back to step S100. This time, an affirmative answer is given at step S110 after the processing of steps S100 to S108 since the engine ECU 50 has started the combustion control of the engine 22. The processing flow then goes to steps S116 to S124. The start of the engine 22 is complete during the repeated execution of steps S100 to S110 and S116 to S124. The processing flow eventually terminates the start control routine of FIG. 3 in response to an affirmative answer at step S124.

In an inadequate state of the exhaust treatment catalyst 161, on the other hand, the CPU 72 executes the processing of and after step S110 in response to a negative answer at step S112. In the inadequate state of the exhaust treatment catalyst 161, the engine ECU 50 immediately starts the combustion control of the engine 22 without waiting for a decrease of the intake pipe pressure P in the air intake conduit 121 to the preset reference negative pressure Pref. In a lower catalyst temperature condition than the specific temperature range, the exhaust treatment catalyst 161 has the insufficient catalytic conversion power and can not sufficiently convert the uncombusted fuel content in the air flow prior to the discharge to the outside air. The early start of the combustion control desirably shortens the time period when the air flow having the uncombusted fuel content is discharged to the outside air without sufficient catalytic conversion, that is, the time period of worsened emission. The uncombusted fuel content in the air flow is ascribed to, for example, slow leakage of the fuel from the injector 126 under the operation stop condition of the engine 22. When the temperature of the internal air of the air intake conduit 121 and the cylinder 150 is lower than the temperature of the exhaust treatment catalyst 161, the low-temperature air flow further decreases the temperature of the exhaust treatment catalyst 161. The early start of the combustion control shortens the time period when the temperature of the exhaust treatment catalyst 161 is lowered. In a higher catalyst temperature condition than the specific temperature range, on the other hand, exposure of the exhaust treatment catalyst 161 to the air accelerates deterioration of the exhaust treatment catalyst 161. The early start of the combustion control desirably shortens the time period when the exhaust treatment catalyst 161 is exposed to the air flow. This effectively prevents the accelerated deterioration of the exhaust treatment catalyst 161.

In the course of drive control in the drive mode with the active combustion control of the engine 22, for example, in the torque conversion drive mode or in the charge-discharge drive mode, the hybrid electronic control unit 70 performs a series of operations as described below. When the exhaust treatment catalyst 161 is in the adequate state, upon satisfaction of a preset engine auto stop condition in the course of the drive control in the drive mode with the active combustion control of the engine 22, the CPU 72 of the hybrid electronic control unit 70 executes engine stop control. The engine stop control sends a stop instruction to the engine ECU 50 to stop the combustion control of the engine 22, while setting the torque commands Tm1* and Tm2* of the motors MG1 and MG2 on the basis of the operation stop of the engine 22 and sending the set torque commands Tm1* and Tm2* to the motor ECU 40. After execution of the engine stop control, the CPU 72 executes the drive control in the motor drive mode or a predetermined vehicle stop control during a stop of the hybrid vehicle 20. When the exhaust treatment catalyst 161 is in the inadequate state, on the other hand, even upon satisfaction of the preset engine auto stop condition, the CPU 72 of the hybrid electronic control unit 70 does not send the stop instruction to the engine ECU 50 to stop the combustion control of the engine 22 but continues the current drive control. The engine auto stop condition is satisfied, for example, when an engine power demand Pe* to be output from the engine 22 is sufficiently low to make the operation efficiency of the engine 2 in a predetermined low efficiency range. The engine power demand Pe* is calculated as the sum of a drive power demand Pr*, a charge-discharge power demand Pb* to be charged into or discharged from the battery 55, and a potential loss Ploss (Pe=Pr*+Pb*+Ploss). The drive power demand Pr* is obtained by dividing the product of the rotation speed Nr of the ring gear shaft 32 a and the torque demand Tr*, which is set corresponding to the input accelerator opening Acc and the input vehicle speed V from the torque demand setting map of FIG. 4, by the gear ratio Gr of the reduction gear 35. The adequate state or the inadequate state of the exhaust treatment catalyst 161 is specified according to the same procedure as step S112 in the start control routine of FIG. 3. When the exhaust treatment catalyst 161 is in the inadequate state, even upon satisfaction of the engine auto stop condition, the hybrid electronic control unit 70 does not stop the combustion control of the engine 22 but keeps the operation of the engine 22. This arrangement desirably reduces the occasions when the exhaust treatment catalyst 161 is in the inadequate state on a start of the engine 22. Namely this effectively reduces the frequency of restarting the operation of the engine 22 in the inadequate state of the exhaust treatment catalyst 161.

The motor MG1 in the hybrid vehicle 20 of the embodiment is equivalent to the motoring device of the invention. The hybrid electronic control unit 70 of the embodiment corresponds to the in-cylinder air flow specification module and the intake pipe pressure specification module of the invention. The hybrid electronic control unit 70 and the engine ECU 50 of the embodiment are equivalent to the internal combustion engine start control module and the internal combustion engine stop control module of the invention. The catalytic converter 160 and the temperature sensor 162 of the embodiment respectively correspond to the exhaust treatment catalyst and the catalyst state detection unit of the invention. The description of the embodiment regarding the operations of the hybrid vehicle 20 simultaneously gives an apparent example of the motor vehicle control method of the invention.

As described above, when the temperature of the exhaust treatment catalyst 161 is in a lower temperature range below the preset low reference temperature or in a higher temperature range above the preset high reference temperature, the hybrid vehicle 20 of the embodiment starts combustion control of the engine 22 including fuel injection control and ignition control, prior to a decrease of the intake pipe pressure P in the air intake conduit 121 to the preset reference negative pressure Pref. This arrangement effectively prevents the potential troubles arising in the course of engine motoring due to a delayed start of the combustion control of the engine 22 in the inadequate state of the exhaust treatment catalyst 161. Such potential troubles include the extended time period of worsened emission and the accelerated deterioration of the exhaust treatment catalyst 161.

In the inadequate state of the exhaust treatment catalyst 161, the control procedure of the embodiment does not allow an auto stop of the engine 22. This arrangement reduces the frequency of restarting the operation of the engine 22 in the inadequate state of the exhaust treatment catalyst, that is, the frequency of restarting the engine 22 with potential shocks.

The hybrid vehicle 20 of the embodiment repeats auto stops and auto starts of the operation of the engine 22 during a drive. The technique of the invention is preferably applicable to such a hybrid vehicle to effectively prevent the potential troubles, for example, the worsened emission and the accelerated deterioration of the exhaust treatment catalyst.

In the adequate state of the exhaust treatment catalyst 161, after a decrease of the intake pipe pressure P in the air intake conduit 121 to the preset reference negative pressure Pref, the combustion control starts to reduce the intake air flow into the cylinder 150. This effectively reduces the potential shocks on a start of the engine 22. In the condition of the gearshift lever 81 set to a P (parking) position, the ring gear shaft 32 a is locked. In this state, the motor MG2 can not output the cancellation torque (=—Tm1*/p) to cancel out the reactive torque applied to the ring gear shaft 32 a. The reactive torque is thus directly applied as a shock to the vehicle body. In the hybrid vehicle 20 of this embodiment, however, in the adequate state of the exhaust treatment catalyst 161, the start control can effectively reduce the potential shocks on a start of the engine 22 even in the condition of the gearshift lever set to the P position. When the exhaust treatment catalyst 161 is not in the inadequate state at the time of starting the engine 22 in the condition of the gearshift lever 81 set to the P position, the start control gives preference to prevention of the potential troubles arising in the course of engine motoring due to the inadequate state of the exhaust treatment catalyst 161, over reduction of the potential shocks on a start of the engine 22.

The reference negative pressure Pref is set to a negative pressure level that is equivalent to the idling operation of the engine 22. In the adequate state of the exhaust treatment catalyst 161, such setting ensures a smooth start of the engine 22 without causing an engine stall.

The embodiment discussed above is to be considered in all aspects as illustrative and not restrictive. There may be many modifications, changes, and alterations without departing from the scope or spirit of the main characteristics of the present invention. Some examples of possible modification are given below.

The start control routine of the embodiment shown in FIG. 3 estimates the intake air flow into the cylinder 150, based on the intake pipe pressure P. This technique is, however, not restrictive, and any other suitable technique may be adopted to estimate the intake air flow into the cylinder 150. In one applicable structure, an in-cylinder pressure sensor is located in the cylinder 150 to measure the internal pressure of the cylinder 150. The intake air flow into the cylinder 150 may be estimated from the internal pressure of the cylinder 150 measured by the in-cylinder pressure sensor. In another applicable structure, an airflow meter is located in the air intake conduit 121 to measure the intake air flow into the engine 22. The intake air flow into the cylinder 150 is directly measured by the airflow meter.

The start control routine of the embodiment shown in FIG. 3 determines whether the intake pipe pressure P in the air intake conduit 121 is lower than the preset reference negative pressure Pref, based on the time t elapsed since a start of motoring at step S108. The determination may alternatively be based on the intake pipe pressure measured by the vacuum sensor 148 set in the air intake conduit 121.

The start control routine of the embodiment shown in FIG. 3 immediately starts the combustion control at step S110, upon specification at step S112 that the exhaust treatment catalyst 161 is in the adequate state. One modified flow of the start control routine may start the combustion control after engine motoring until the intake pipe pressure P decreases to a medium negative pressure level, which is higher than the preset reference negative pressure Pref by a specific pressure level.

In the hybrid vehicle 20 of the embodiment, in the inadequate state of the exhaust treatment catalyst 161, even upon satisfaction of the engine auto stop condition, the control procedure does not allow an auto stop of the engine 22. One possible modification may allow an auto stop of the engine 22 even under such conditions at a reduced frequency. The modified procedure counts the number of times of satisfaction of the engine auto stop condition and allows an engine auto stop at each even number of times but prohibits the engine auto stop at each odd number of times.

The above embodiment regards application of the invention to the hybrid vehicle 20. The technique of the invention is also applicable to a vehicle with a simple idling stop function that prevents transmission of the output powers of motors MG1 and MG2 to a driveshaft.

The present invention claims the benefit of priority from Japanese Patent Application No. 2005-107429 filed on Apr. 4, 2005, the entire contents of which are incorporated by reference herein. 

1. A motor vehicle, comprising: a motoring device that is capable of motoring an internal combustion engine; an exhaust treatment catalyst that treats exhaust of the internal combustion engine to convert harmful components of the exhaust into harmless components; a catalyst state detection unit that detects a state of the exhaust treatment catalyst; an in-cylinder air flow specification module that specifies whether an intake air flow into a cylinder of the internal combustion engine decreases to a preset low range; and an internal combustion engine start control module that starts combustion control of the internal combustion engine, in response to requirement for a restart of the internal combustion engine, when the state of the exhaust treatment catalyst detected by the catalyst state detection unit is a preset adequate state, said internal combustion engine start control module starting the combustion control of the internal combustion engine after specification of a decrease in intake air flow into the cylinder of the internal combustion engine to the preset low range by said in-cylinder air flow specification module in the course of motoring the internal combustion engine by the motoring device, when the state of the exhaust treatment catalyst detected by the catalyst state detection unit is not the preset adequate state but is an inadequate state, said internal combustion engine start control module immediately starting the combustion control of the internal combustion engine, prior to specification of a decrease in intake air flow into the cylinder of the internal combustion engine to the preset low range by said in-cylinder air flow specification module in the course of motoring the internal combustion engine by the motoring device.
 2. A motor vehicle in accordance with claim 1, wherein the preset low range represents a certain level of the intake air flow into the cylinder that is equivalent to idling operation of the internal combustion engine.
 3. A motor vehicle in accordance with claim 1, said motor vehicle further comprising: an intake pipe pressure specification module that specifies whether an intake pipe pressure of the internal combustion engine decreases to a preset reference negative pressure, wherein said in-cylinder air flow specification module specifies whether the intake air flow into the cylinder of the internal combustion engine decreases to the preset low range, based on a result of the specification of whether the intake pipe pressure of the internal combustion engine decreases to the preset reference negative pressure.
 4. A motor vehicle in accordance with claim 3, wherein the preset reference negative pressure represents a certain level of the intake pipe pressure that is equivalent to idling operation of the internal combustion engine.
 5. A motor vehicle in accordance with claim 3, wherein said intake pipe pressure specification module specifies whether the intake pipe pressure of the internal combustion engine decreases to the preset reference negative pressure, based on a specific parameter in correlation to the intake pipe pressure of the internal combustion engine.
 6. A motor vehicle in accordance with claim 5, wherein the specific parameter is a motoring time of the internal combustion engine by the motoring device.
 7. A motor vehicle in accordance with claim 1, wherein the catalyst state detection unit detects the inadequate state of the exhaust treatment catalyst, when the exhaust treatment catalyst has a temperature in a low temperature range that allows exertion of only an insufficient catalytic conversion power.
 8. A motor vehicle in accordance with claim 1, wherein the catalyst state detection unit detects the inadequate state of the exhaust treatment catalyst, when the exhaust treatment catalyst has a temperature in a high temperature range that causes quick deterioration of the exhaust treatment catalyst by exposure to the air.
 9. A motor vehicle in accordance with claim 1, said motor vehicle further comprising an internal combustion engine stop control module that stops the operation of the internal combustion engine upon satisfaction of a preset internal combustion engine auto stop condition, wherein said internal combustion engine start control module restarts the internal combustion engine upon satisfaction of a preset internal combustion engine auto start condition after the stop of the operation of the internal combustion engine by said internal combustion engine stop control module.
 10. A motor vehicle in accordance with claim 9, wherein said internal combustion engine stop control module prohibits the stop of the internal combustion engine when the exhaust treatment catalyst is not in the preset adequate state during operation of the internal combustion engine.
 11. A motor vehicle, comprising: a motoring device that is capable of motoring an internal combustion engine; an exhaust treatment catalyst that treats exhaust of the internal combustion engine to convert harmful components of the exhaust into harmless components; a catalyst state detection unit that detects a state of the exhaust treatment catalyst; an intake pipe pressure specification module that specifies whether an intake pipe pressure of the internal combustion engine decreases to a preset reference negative pressure; and an internal combustion engine start control module that starts combustion control of the internal combustion engine, in response to requirement for a restart of the internal combustion engine, when the state of the exhaust treatment catalyst detected by the catalyst state detection unit is a preset adequate state, said internal combustion engine start control module starting the combustion control of the internal combustion engine after specification of a decrease in intake pipe pressure of the internal combustion engine to the preset reference negative pressure by said intake pipe pressure specification module in the course of motoring the internal combustion engine by the motoring device, when the state of the exhaust treatment catalyst detected by the catalyst state detection unit is not the preset adequate state but is an inadequate state, said internal combustion engine start control module immediately starting the combustion control of the internal combustion engine, prior to specification of a decrease in intake pipe pressure of the internal combustion engine to the preset reference negative pressure by said intake pipe pressure specification module in the course of motoring the internal combustion engine by the motoring device.
 12. A motor vehicle in accordance with claim 11, wherein the preset reference negative pressure represents a certain level of the intake pipe pressure that is equivalent to idling operation of the internal combustion engine.
 13. A motor vehicle in accordance with claim 11, wherein said intake pipe pressure specification module specifies whether the intake pipe pressure of the internal combustion engine decreases to the preset reference negative pressure, based on a specific parameter in correlation to the intake pipe pressure of the internal combustion engine.
 14. A motor vehicle in accordance with claim 13, wherein the specific parameter is a motoring time of the internal combustion engine by the motoring device.
 15. A motor vehicle in accordance with claim 11, wherein the catalyst state detection unit detects the inadequate state of the exhaust treatment catalyst, when the exhaust treatment catalyst has a temperature in a low temperature range that allows exertion of only an insufficient catalytic conversion power.
 16. A motor vehicle in accordance with claim 11, wherein the catalyst state detection unit detects the inadequate state of the exhaust treatment catalyst, when the exhaust treatment catalyst has a temperature in a high temperature range that causes quick deterioration of the exhaust treatment catalyst by exposure to the air.
 17. A motor vehicle in accordance with claim 11, said motor vehicle further comprising an internal combustion engine stop control module that stops the operation of the internal combustion engine upon satisfaction of a preset internal combustion engine auto stop condition, wherein said internal combustion engine start control module restarts the internal combustion engine upon satisfaction of a preset internal combustion engine auto start condition after the stop of the operation of the internal combustion engine by said internal combustion engine stop control module.
 18. A motor vehicle in accordance with claim 17, wherein said internal combustion engine stop control module prohibits the stop of the internal combustion engine when the exhaust treatment catalyst is not in the preset adequate state during operation of the internal combustion engine.
 19. A control method of a motor vehicle, comprising the steps of: (a) detecting a state of an exhaust treatment catalyst that treats exhaust of the internal combustion engine to convert harmful components of the exhaust into harmless components; and (b) when the state of the exhaust treatment catalyst detected by the step (a) is a preset adequate state, starting the combustion control of the internal combustion engine after specification of a decrease in intake air flow into the cylinder of the internal combustion engine to the preset low range, in the course of motoring the internal combustion engine, and when the state of the exhaust treatment catalyst detected by the step (a) is not the preset adequate state but is an inadequate state, starting the combustion control of the internal combustion engine, prior to specification of a decrease in intake air flow into the cylinder of the internal combustion engine to the preset low range in the course of motoring the internal combustion engine.
 20. A control method of a motor vehicle, comprising the steps of: (a) detecting a state of an exhaust treatment catalyst that treats exhaust of the internal combustion engine to convert harmful components of the exhaust into harmless components; and (b) when the state of the exhaust treatment catalyst detected by the step (a) is a preset adequate state, starting the combustion control of the internal combustion engine after specification of a decrease in intake pipe pressure of the internal combustion engine to the preset reference negative pressure in the course of motoring the internal combustion engine, and when the state of the exhaust treatment catalyst detected by the step (a) is not the preset adequate state but is an inadequate state, starting the combustion control of the internal combustion engine, prior to specification of a decrease in intake pipe pressure of the internal combustion engine to the preset reference negative pressure in the course of motoring the internal combustion engine. 